Stromatolites, beings 3.5 billion years old, cluster in Patagonia, with a structure very similar to their ancient fossils — and were only found now
14 Dec 2023 – 9:03 pm
(updated on 12/15/2023 at 01:22 am)
Microbial communities that are among the planet’s earliest life forms have been found in previously unknown Patagonian lagoons, both living and fossilized. These are stromatolites, microscopic formations that, when agglomerated, reach considerable sizes. Its fossils are among the first evidence of living beings3.5 billion years old — and the specimens seen in Argentina are especially similar to their ancestors.
Photo: Diego Delso/CC-BY-SA-4.0 / Canaltech
Several species use the stromatolite type of formation to cluster together, with the most common being cyanobacteria. These life forms produce oxygen, which was rare in Earth’s ancient atmosphere, so the first stromatolites are probably quite different from today’s ones, made of sulfate-reducing bacteria. Both types form piles of photosynthesizing organisms that use sand and their own liquids to solidify and grow in search of sunlight.
 
Modern-day stromatolites reach more than a meter in height, but are vulnerable to predators and other organisms that outgrow them. Therefore, these beings generally only survive where other forms of life cannot, such as brackish waters. The most famous are from Shark Bay, Australia, who live next to their fossilized ancestors, among the oldest on the planet.
Primitive life in Patagonia
Puna de Atacama, in Patagonia, is 4,000 meters above sea level, and its hypersaline lagoons are home to an impressive discovery — one that had gone unnoticed by scientists until today. The remote area could only be found with a 9-hour drive on dirt roads, with the researchers responsible having to stay in a village of 35 inhabitants fed only by a water spring, as rain is too rare to guarantee the liquid.
Satellite images revealed the lagoons 16 km from the village, visited only on the scientists’ last day at the site, as the target of the study was other bacteria, used in soil remediation. The 12 lagoons occupy an area of 10 hectares (or 100,000 km²) with transparent waters, with very little life and mud. It was by looking to the bottom that living stromatolites larger than anyone had ever seen were revealed, 5 meters wide and tens of centimeters high (although larger fossils exist).
Stromatolites may have been the first form of life to be preserved in fossils, 3.5 billion years old — they are clusters of bacteria that form rocks, like this example from the UFRJ Museum (Image: Acervo do Museu Nacional/UFRJ/ CC-BY-4.0)
Foto: Canaltech
Chemical analysis of the interior revealed a unique composition, unheard of elsewhere—gypsum (CaSO42H2O), for the most part, which is common in fossil stromatolites but never seen in living specimens. The surface turned out to be composed of cyanobacteria, with a pink center due to the abundance of archaea, unicellular microorganisms without a nucleus that are strong candidates for having composed the original stromatolites.
The place is very saline and acidic, with sunlight barely being filtered by the lower atmosphere — very similar to early Earth, according to scientists. The Atacama Desert has been visited by several astrobiologists as it is the closest place to the ancient atmosphere of Mars. Studying the beings that survive or were fossilized in this environment helps us know what to expect when we scour Martian rocks for signs of life.
Scientists, however, consider the discovery almost too late, as the Atacama is full of lithium. In the past, the material was despised, but it is now coveted by mining companies as it is an important ingredient in batteries. The area is about to be drilled in search of deposits of the element, and this in itself could be enough to destroy the stromatolite system, which is quite sensitive to changes.
Source: American Geophysical Union Fall Conference, Mashable
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2023-12-15 00:03:52
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